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PAR-Eckert Cold Storage,Manteca,CA November 25,2002 ' Page 9 laboratory analyses on groundwater samples collected from the well have been reported by WHF and Condor. Historic laboratory analysis of groundwater samples collected from the on-site domestic well indicated that the well has not been impacted by petroleum hydrocarbons. Laboratory analytical results for the on-site domestic well collected by Condor during quarterly groundwater monitoring events are included in Appendix B. ' 9.0 DISCUSSION OF RESULTS Laboratory analytical data indicate that the groundwater is the predominant mechanism for contaminant ' distribution. The highest concentrations of gasoline and BTEX in the groundwater were identified in the vicinity of the UST area and northwest of the UST area (down-gradient). In the vadose zone soils, the highest concentrations of BTEX and TPH-G were identified in the vicinity of the UST area, at ' approximately 15 to 20 feet bgs, and typically decreased with depth in the borings advanced at the site. Laboratory analyses of the soil samples (MW-1 through MW-8; B-1 through B-4) and groundwater samples collected from the saturated zones in the CPT boring CPT-1 indicate that concentrations of 1,2- DCA, MTBE, and BTEX compounds generally decreased with depth. The greatest concentrations of contaminants appear to be at, or near, the groundwater surface and attenuate with depth. BTEX and TPH- 1 G were detected in the deepest soil sample (55 feet bgs) collected from B-3. Hydrocarbon constituents were detected in the deepest groundwater sample(100-104 feet bgs) collected from CPT-1. ' The approximate lateral extent of 1,2-DCA, MTBE and total BTEX contamination in site groundwater is shown in Figures 5, 6, and 7, Appendix A. The approximate vertical extent of 1,2-DCA, MTBE and total BTEX contamination in site groundwater is depicted Figures 11 through 16, Appendix A. Laboratory ' . analyses of the groundwater samples collected from the saturated zone in CPT-1 suggests that contamination extends to at least approximately 104 feet bgs but appears to attenuate substantially in the vicinity of that depth. ' 9.1 DESCRIPTION OF CORRECTIVE ACTION STRATEGIES Evaluation of the remedial alternatives for soil and groundwater at the site is presented below. The remedial alternatives are limited by the site use constraints. Based on the contaminants of concern and the limitations noted, the following alternatives have been considered: ' 1. In situ attenuation through passive biodegradation; 2. Enhanced in situ bioremediation and/or chemical oxidation; 3. Soil Vapor Extraction; 4. Air Sparging; 5. Ex situ groundwater treatment(pump and treat); and b. Combinations of Alternatives 2 through 5. ' Alternative 1, in situ attenuation through passive biodegradation, would rely on natural biodegradation of the volatile organic compounds in the soil and water. Conceptually, the native bacteria would rely on the petroleum hydrocarbons for their carbon source and the nutrients and oxygen dissolved in the groundwater to enhance the bacterial activity. The time required to achieve acceptable water quality cannot be estimated and there would be no down-gradient containment of the plume; however, costs would be limited to those for groundwater monitoring and monitoring for natural attenuation. Alternative 2, enhanced in situ bioremediation and/or chemical oxidation, would augment the natural biodegradation discussed above. Augmentation can involve nutrients, specially developed microbes, .y CONDOR 1